1. Field of the Invention
The present invention relates to: a data holding circuit capable of latching an input signal at both a rising edge timing and a falling edge timing of a clock signal; and a signal processing circuit used in the data holding circuit for communication and for reading data from a variety of disks.
2. Description of the Related Art
Serial communications capable of transmitting and receiving data at a high speed have been recently used when communications are conducted in a wired or wireless manner. For example, USB (Universal Serial Bus) utilized for connection between a computer and a peripheral device thereof, and Serial ATA (Advanced Technology Attachment) for connection with a hard disk or the like are used for a wired communication. IrDA (Infrared Data Association; infrared communication) or the like is used for a wireless communication. In addition, serial signals in similar serial communications are used for the reading of data from a variety of disks.
Receiving circuits used for the communications described above and reading circuits used for the reading of data from disks generally require a clock signal having a frequency three times or more as high as that for a communication rate or a reading rate. In order to perform the aforementioned processes at a high precision, it is necessary to set a frequency of a reference clock signal as high as possible. However, when a clock signal having a high frequency is used, problems of increasing a current consumption, increasing unnecessary radiation noise and the like occur.
Thus, in order to address these problems, data has been conventionally sampled at both a rising edge timing and a falling edge timing of a clock signal. This corresponds to a case when a clock signal having a frequency twice as high is used. As such, a clock signal having the same frequency as conventional has been used in order to improve the precision of processes, and a clock signal having a frequency that is one-half of a conventional frequency has been used in order to reduce a current consumption and unnecessary radiation noise at a precision equivalent to the conventional.
[Reference 1] Japanese Laid-Open Publication No. 4-105415